Screening for Colorectal Neoplasms

Colorectal cancer is ideal for screening because it is a common disease affecting 6% of men and women that is fatal in almost 50% of cases yet is curable if detected at an earlier stage. Furthermore, the vast majority of cases arise from benign adenomas that progress over many years to cancer, and removal of adenomas has been shown to prevent the vast majority of cancers. Colorectal cancer screening has now been endorsed by the United States Preventive Services Task Force, the Agency for Health Care Policy and Research, the American Cancer Society, and every professional gastroenterology and colorectal surgery society. Although there is continued debate about the optimal cost-effective means of providing population screening, there is unanimous consent that screening of some kind should be offered to every patient over the age of 50 years. Several analyses suggest that the cost of screening is approximately $25,000 per year of life saved for all recommended screening strategies, which is well below the range of $40,000-$50,000 per year generally considered to be cost-effective.

A number of options for screening are available and reimbursed by third-party payers and by Medicare. Patients with first-degree relatives with colorectal cancer are at increased risk, and for these individuals more intensive screening recommendations are recommended.

The advantages and disadvantages of the various options are discussed below. It is important for primary care providers to understand the relative merits of various options and to discuss them with their patients. Despite growing awareness of the importance of screening on the part of medical professionals and the public, less than 50% of patients have undergone screening of any kind. Discussion and encouragement by the primary care provider are the most important factors in achieving patient compliance with screening programs. The potential for harm from screening must be weighed against the likelihood of benefit, especially in elderly patients with comorbid illnesses and shorter life expectancy.

A. Fecal Occult Blood Test or Multitarget DNA Assay

Most colorectal cancers and some large adenomas result in increased chronic blood loss that may be detectable. A variety of tests have been developed that have varying sensitivities for fecal occult blood, some of which are in clinical testing. A guaiac-based test (Hemoccult II) has undergone the most extensive testing and has had the greatest clinical use. Two slides must be prepared from three consecutive bowel movements. To reduce the likelihood of false-positive tests, patients should abstain from aspirin (in doses greater than 325 mg/d), NSAIDs, red meat, poultry, fish, and vegetables with peroxide activity (turnips, horseradish) for 72 hours. Vitamin C may cause a false-negative test. Slides should be developed within 7 days after preparation. The World Health Organization recently endorsed another guaiac test for FOBT, Hemoccult Sensa, because it has higher sensitivity than the Hemoccult II test; however, data from large clinical trials with this test are lacking.